The present invention relates to an optical information recording medium of a sealed type comprising a pair of disc-shaped substrates and a recording layer formed thereon for recording therein optical information and reproducing the same therefrom.
Conventionally, when fabricating an optical information recording medium including a recording layer comprising an organic dye compound by sealing a pair of disc-shaped substrates and a spacer interposed therebetween, an epoxy adhesive agent is employed. A conventional epoxy adhesive agent is advantageous over other adhesive agents in that it decreases neither the reflection ratio nor the S/N ratio of the recording material of the recording medium. However, since the epoxy adhesive agent is a thermosetting adhesive agent, there is the risk that the substrate is deformed during the application of heat for hardening the epoxy adhesive agent. Further, the epoxy adhesive agent has the shortcoming that the productivity of the recording medium is not good because an extended period of time is required for the hardening of the adhesive agent, and a jig is necessary for fixing the substrates, spacer and other members during the hardening.
In order to avoid the above shortcomings, a novel adhesive agent comprising an ultraviolet-ray-hardening resin containing a radical polymerization initiator is recently used. This novel adhesive agent does not have the shortcomings of the above-mentioned epoxy adhesive agent, but it does have the shortcoming that the reflection ratio of the recording member of the disc-shaped recording medium, or the S/N ratio thereof is decreased by an unhardened portion of the adhesive agent which is pressed out from the sealed portions.
Further, adhesive agents comprising an epoxy resin containing a cationic photo-polymerization initiator comprising an onium salt, such as triaryl sulfonium salt, dialkylphenaoyl sulfonium salt, dialkyl-4-hydroxyphenyl sulfonium salt, and diaryl iodonium salt, with a counter ion such as SbF.sub.6.sup..crclbar., BF.sub.4.sup..crclbar., PF.sub.6.sup..crclbar., and AsF.sub.6.sup..crclbar., have been proposed for the above sealing. These adhesive agents do not have the problem that the pressed out portion of the adhesive agent is not hardened, but has the shortcoming that a strong acid containing any of the above counter ions is produced during the hardening process of the adhesive agent and the organic dye compound contained in the recording layer of the recording medium is damaged by the strong acid.
In order to solve the above problem of the adhesive agent, the inventors of the present invention proposed an adhesive agent comprising (i) an epoxy resin component and (ii) a composite catalyst comprising a photo-decomposing organic silicone compound and a metal complex in Japanese Laid-Open patent application No. 62-259245. This adhesive agent is hardened by photo-cationic polymerization and the hardening thereof is particularly quick when alicyclic epoxy resins are employed. This adhesive agent, however, has the shortcoming that some of the epoxy resins have an adverse effect on the organic dye compound contained in the recording medium, and this shortcoming cannot be completely eliminated. In particular, the following epoxy resins are not suitable for use with the organic dye compounds. ERU 2021, 3000, 3000, EHPE 3150-1 (made by Daicel Chemical Industries, Ltd.); ERL 4206 and ERU 4234 (made by Union Carbide Corp.), and ##STR3## It is reported that ERU 4234 is a skin-cancer-causing material.